The effects of protein synthesis inhibitors on theGonyaulax clock

Summary Cycloheximide has been shown to be potent in phase-shifting the circadian glow rhythm of the dinoflagellateGonyaulax polyedra. In experiments in which the cells were exposed to drug pulses of varying concentration (0.35 M to 10 M) and duration (0.5 h to 8 h), the phase shift produced was linear with the log of the product of pulse strength and duration. The sensitivity to drug-induced phase shifting varies as a function of time of day; both advances and delays occurred and, depending on the strength of the perturbation, resulted in strong or weak-type phase response curves. Pulses given at different times after the light/dark to constant dim transition resulted in a crossover from delays to advances at about 15.5 h; this crossover point was the same at 19 °C and 24°C. The occurrence of extended transients following cycloheximide-induced phase advances (but not delays) appears to be the first example of such transients in a microbial circadian system.This research was supported in part by a grant from the National Institutes of Health (GM-19536). J.D. was a NIH predoctoral trainee (T01-GM 00036 and NRSA T32-GM 07598)